Just over half of the congressional districts in the country have shares of their population under age 5 that are greater than or equal to the national average of 6.4 percent. States with higher percentages of their population under age 5 tend to be found in the West and South. Utah's 3rd congressional district has the highest percentage of young children in its population, with 10.5 percent, and California's 30th has the lowest, at 4 percent.

Population growth in successive decades has followed different trends for states across the country. While many states had early, substantial growth in percentage terms most of that population growth was quite small in numeric terms. In contrast, states with high percentage growth in more recent decades also gained very large numbers of people.

Passing through some of the most sparsely populated territory in the country, I-90 connects Seattle, Chicago, Cleveland, Buffalo, and Boston. Selected cities along the route are labeled, for reference, with cities of 250,000 or more shown in bold and with filled circles.

Median household income varies by county across the United States. Predominantly rural counties across parts of the South, Southwest, Midwest, and Appalachia have some of the lower median incomes in the country. Counties with higher median household incomes are generally located in the Boston-to-Washington corridor, in larger metropolitan statistical areas, and along the coasts.